The present invention relates generally to a flow regulation apparatus, and more particularly, to a one-way check valve which will open at very low pressures to allow high flow rates in a first direction and which will close to prevent flow in a second direction.
One requirement of one-way flow valves, such as the type used as check valves in positive crankcase ventilation systems for internal combustion engines, is that the valves must offer little resistance to fluid flow in one direction but will completely stop fluid flow in the opposite direction. A valve which is commonly used for this purpose is a poppet valve which comprises an axially movable valve member which is typically biased toward a valve seat by a helical spring. This type of valve suffers from the problem of requiring numerous structural elements to maintain the alignment of the movable valve member and to provide the biasing force to close the valve. In addition, the weight of the movable valve member results in this member having too much inertia to respond quickly to sudden changes in direction of the fluid flow at low pressures.
Another valve which is known in the art for limiting flow in one direction and providing a high flow rate is the umbrella valve. In the umbrella valve, the movable valve member is formed of a flexible material and has a generally curved cross-section. Hoop stresses in the radially outer portions of the valve member produce the spring force biasing the valve closed which must be overcome to open the valve. Thus, umbrella valves are designed to initially open at a small predetermined pressure and subsequently open further to provide a large flow rate with an increase in pressure.
In other applications, such as valves used in artificial respiration devices, a duckbill check valve may be used in combination with a diaphragm member to forcibly convey air to a patient from an air bag, while preventing exhaled air from being returned to the bag. In such an application, the valve must also be capable of preventing back flow of fluids such as vomit. Known respirator valves typically produce too much resistance to the flow from the bag to the patient, which in turn creates excessive back pressure within the bag such that attending personnel applying squeezing force to the bag will tire quickly. In addition, respiration devices incorporating duckbill valves often produce an objectionable honking noise.
While known check valves are satisfactory for many applications, the ability of known valves to respond at low pressures typically decreases as the size of the valve and the volume of fluid flow conducted by the valve is increased. Thus, there exists a need for a valve which is capable of permitting high fluid flow rates at very low pressures. In addition, there exists a need for a valve which will open and close quickly in response to changes in direction of the fluid flow and which will not collapse when subjected to high pressures in a reverse flow condition.
Further, there is a need for a valve which is capable of quiet operation while providing high flow rates at very low pressures and which may be incorporated into conventional structure for artificial respiration devices.